PURIFICATION AND CHARACTERIZATION OF CAMPYLOBACTER-RECTUS SURFACE-LAYER PROTEINS

Campylobacter rectus is a putative periodontopathogen which expresses a proteinaceous surface layer (S-layer) external to the outer membrane , S-layers are considered to play a protective role for the microorgan ism in hostile environments, The S-layer proteins from six different C . rectus strains (five human isolates and a nonhuman primate [NHP] iso late) were isolated, purified, and characterized, The S-layer proteins of these strains varied in molecular mass (ca, 150 to 166 kDa) as det ermined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, They all reacted with monospecific rabbit antiserum to the purified S- layer of C. rectus 314, but a quantitative enzyme-linked immunosorbent assay demonstrated a strong antigenic relationship among the five hum an strains, while the NHP strain, 6250, showed weaker reactivity, Amin o acid composition analysis showed that the S-layers of four C. rectus strains contained large proportions of acidic amino acids (13 to 27%) and that >34% of the amino acid residues were hydrophobic. Amino acid sequence analysis of six S-layer proteins revealed that the first 15 amino-terminal amino acids were identical and showed seven residues of identity with the amino-terminal sequence of the Campylobacter fetus S-layer protein SapAl, CNBr peptide profiles of the S-layer proteins f rom C. rectus 314, ATCC 33238, and 6250 confirmed that the S-layer pro teins from the human strains were similar to each other and somewhat d ifferent from that of the NHP isolate (strain 6250), However, the S-la yer proteins from the two human isolates do show some structural heter ogeneity, For example, there was a 17-kDa fragment unique to the C. re ctus 314 S-layer, The amino-terminal sequence of this peptide had homo logy with the C. rectus 51-kDa porin and was composed of nearly 50% hy drophobic residues, Thus, the S-layer protein from C. rectus has struc tural heterogeneity among different human strains and immunoheterogene ity with the NHP strain.